Technical Abstract:
Listeria monocytogenes is a gram-positive food-borne bacterial pathogen of humans and other vertebrate species. In healthy adults, the disease can be mild and self-limiting, in the form of flu-like symptoms or gastroenteritis. However, in newborn children, pregnant women, the elderly, and immunocompromised individuals, the disease symptoms can manifest into bacteremia, miscarriage, bacterial endocarditis, spesis, meningoencephalitis and death. Listeria outbreaks are typically sporadic, and are associated with consumption of various food products that are contaminated by the pathogen. At least 16 serotypes of L. monocytogenes have been identified, three of which (1/2/a, 1/2b and 4b) are responsible for most human cases of listerosis. Strains of serotype 4b are responsible for numerous sporadic cases and most major outbreaks of listeriosis. To better understand the molecular mechanisms of virulence in humans, and survival of the pathogen at various points along the food chain The Institute for Genomic Research and the USDA-ARS sequenced by the whole genome random shotgun method and closed and annotated the genome of L. monocytogenes strain F2365 (serotype 4b, Mexican-style cheese isolate). To characterize the genetic variability of L. monocytogenes, strain H7858 (serotype 4b, frankfurter isolate)and strain F6854 (serotype 1/2a, turkey frankfurter isolate)are currently being sequenced to 8X coverage and compared to the closed and annotated L. monocytogenes genomes. Preliminary analysis of the closed F2365 genome indicated a size of 2,905,310 bp, which is smaller than the previously sequenced EGD-e strain (serotype 1/2a, animal isolate; 2,944,528 bp). One major difference to account for the size discrepancy is the absence of an A118-like prophage (ca 42 kbp). Additionally, results from various BLAST analyses have revealed that strain F2365 contained ca 124 putative open reading frames (ORFs) that were absent from strain EGD-e, whereas strain EDG-e contained ca 128 putative ORFs that were absent from strain F2365.